The leader of Spain`s wealthy Catalonia region signed a decree on Monday calling early parliamentary elections on September 27 which he has said will act as proxy vote on independence.

The decree signed by Catalan president Artur Mas made no reference to independence for the northeastern region, which is home to 7.5 million people and accounts for a fifth of Spain`s economic output.

But Mas -- who already faces criminal charges for staging a mock independence referendum in November despite objections from the central government -- has said that if pro-secession parties win a majority, they will aim to split from Spain within 18 months.

"Politically they will not be normal elections, politically they are a plebiscite on Catalan freedom and sovereignty," he said Thursday.

Spain`s conservative central government fiercely rejects the idea that the Catalan elections should be interpreted as a referendum on independence.

Deputy Prime Minister Soraya Saenz de Santamaria said that under the constitution the vote can only be about selecting a new Catalan parliament.

"In a regional election one chooses lawmakers for the regional parliament, who in turn elect a president of the region. This is what citizens are deciding with this vote and nothing else," she told a news conference earlier on Monday.

Support for secessionist groups in Catalonia has weakened due to political infighting and the emergence of popular parties, such as the far-left Podemos, more interested in social and economic issues.

But in July, Catalan pro-independence parties set aside their differences and agreed to run on a joint ticket in the regional polls, breathing new life into the movement.

The joint list, called "Together for Yes", includes the Mas` ruling CDC party, the left-wing separatist ERC and associations which have organised massive pro-independence demonstrations in the region.

Catalonia`s three pro-independence parties could capture 68 to 72 seats in the region`s 135-seat parliament, according to a poll published July 12 in Catalan daily La Vanguardia.